Conventionally, it has been known that a liquid crystal display panel is used in a projector for projecting an image onto a screen. In recent years, it has been known in the projector that a micro-lens array substrate including a micro-lens array on a liquid crystal display panel is used to improve the utilization efficiency of light in view of demand for a highly accurate and highly definite image.
FIG. 3 is a front view showing a schematic structure of a liquid crystal projector mounting a conventional micro-lens array substrate. FIG. 4 is a front view showing a substantial part in the micro-lens array substrate of the liquid crystal projector.
As shown in FIGS. 3 and 4, the liquid crystal projector includes a white light source 11, a condensing lens 12, a dichroic mirror 13, a micro-lens array substrate 14, a liquid crystal panel 15, a field lens 16, and a projection lens 17, and the liquid crystal projector projects an image onto a screen 18.
Light emitted from the white light source 11 passes through the condensing lens 12 and turns to parallel light beams. The light beams are illuminated to the dichroic mirror 13. The dichroic mirror 13 is composed of dichroic mirrors 13R, 13G, and 13B of three types, which are disposed with respectively different angles. The dichroic mirrors 13R, 13G, and 13B have such characteristics that they selectively reflect light beams of respective wavelength ranges corresponding to red, green, and blue and transmit the light of other wavelength range. The dichroic mirrors 13R, 13G, and 13B are aligned in the optical axis in the order of red, green, and blue, i.e. in this order.
In the liquid crystal projector, light beams 19 divided by the dichroic mirrors 13R, 13G, and 13B are incident on the micro-lens array substrate 14 at respectively different angles. The light beams 19, which have passed through the micro-lens array substrate 14, pass through the respectively corresponding apertures on the liquid crystal panel 15. Thereafter, the light beams 19 are caused to change their optical axes and projected via the projection lens 17 onto the screen 18.
However, the micro-lens array substrate 14 has the following problems.
After the light beams 19, which have been focused onto the apertures of the liquid crystal panel 15 by the micro-lens array substrate 14, pass through the liquid crystal panel 15, they diverge with great angles in an expanding manner. Without employing a projection lens 17 with a large diameter, this causes a decline in the utilization efficiency of light, resulting in a lowering in picture quality.
In order to solve the above problem, for example, U.S. Pat. No. 5,633,737 (Japanese Laid-Open Patent Publication 181487/1995 (Tokukaihei 7-181487; published on Jul. 21, 1995)) has disclosed, as shown in FIG. 5, that a second micro-lens array 23 is disposed between a liquid crystal panel 21 and a first micro-lens array 22, and the respective optical axes of light beams 24, which has been focused onto the first micro-lens array 22 on the light beam entering side, are changed by the second micro-lens array 23 so as to be parallel to one another in outgoing the second micro-lens array 23, which suppresses divergence of the light beams 24, thus improving the utilization efficiency of light without using a projection lens with a large diameter.
Moreover, for example, Japanese Laid-Open Patent Publication 2000-147500 (Tokukai 2000-147500; published on May 26, 2000) has disclosed a method for manufacturing a double-layer structured micro-lens array substrate.
The following description will be given based on a method for manufacturing the double-layer structured micro-lens array substrate with reference to FIGS. 6a through 6h. 
As shown in FIGS. 6a through 6h, first of all, a first ultraviolet-hardening resin 39 is supplied on a stamper 35 formed with a reversal pattern of a first micro-lens array 32 (FIG. 6a). Next, the first ultraviolet-hardening resin 39 is pressed by a glass substrate 37 to spread between the stamper 35 and the glass substrate 37. Thereafter, the first ultraviolet-hardening resin 39 is hardened by ultraviolet irradiation through the glass substrate 37 (FIG. 6b), thereby forming the first micro-lens array 32. Then, the first micro-lens array 32 that has been hardened is separated from the stamper 35 (FIG. 6c).
Additionally, a second micro-lens array 33 is formed in the same manner as the first micro-lens array 32. Specifically, first of all, a first ultraviolet-hardening resin 39 is supplied on a stamper 36 formed with a reversal pattern of the second micro-lens array 33 (FIG. 6d). Next, the first ultraviolet-hardening resin 39 is pressed by a glass substrate 38 to spread between the stamper 36 and the glass substrate 38. Thereafter, the first ultraviolet-hardening resin 39 is hardened by ultraviolet irradiation through the glass substrate 38 (FIG. 6e), thereby forming the second micro-lens array 33. Then, the second micro-lens array 33 that has been hardened is separated from the stamper 36 (FIG. 6f).
Subsequently, a second ultraviolet-hardening resin 40 is supplied on the second micro-lens array 33 that has been formed on the glass substrate 38 (FIG. 6g). The second ultraviolet-hardening resin 40 is pressed by the glass substrate 37 with the first micro-lens array 32 faced down, and a distance between the micro-lens arrays 32 and 33 is adjusted. Thereafter, the second ultraviolet-hardening resin 40 is hardened by ultraviolet irradiation, thereby forming a micro-lens array substrate (FIG. 6h).
However, the following problem occurs in the above-described method for manufacturing a double-layer structured micro-lens array substrate.
Specifically, in the manufacturing method disclosed in Japanese Laid-Open Patent Publication 2000-147500, a micro-lens array substrate is made up in such a manner that the glass substrates 37 and 38 on which the first micro-lens arrays 32 and 33 are respectively provided are separately generated, and thereafter, the two glass substrates are joined together. However, the publication has not disclosed and taught an alignment of the micro-lens arrays. Directly joining the first and second micro-lens arrays 32 and 33 together without some kind of arrangements causes deviation in optical axes and inclination of the first and second micro-lens arrays 32 and 33, resulting in a decline in the utilization efficiency of light and a lowering of resolution due to mixed colors of the light beams.
In order to solve this problem considered is a method of mounting the glass substrates on die sets and joining the glass substrates together. The following description will be given based on concrete examples of a method for manufacturing a micro-lens array using the die sets (first and second methods).
In the first method, as shown in FIGS. 7a through 7c, the glass substrate 37 on which the first micro-lens array 32 is formed is fixed on an upper stage 201 of the die sets, and a glass substrate 38 on which the second micro-lens array 33 is formed is fixed on a lower stage 202 of the die sets (FIG. 7a). After the second ultraviolet-hardening resin 40 is supplied on the glass substrate 38 (FIG. 7b), the upper stage 201 and the lower stage 202 are caused to move closer to each other to spread the second ultraviolet-hardening resin 40 between the first and second micro-lens arrays (FIG. 7c). Thereafter, the second ultraviolet-hardening resin 40 is hardened by ultraviolet irradiation. This arrangement makes it possible to join the glass substrates 37 and 38 together with their parallelism maintained.
Moreover, in the second method for manufacturing a double-layer structured micro-lens array substrate, as shown in FIGS. 8a through 8f, between the upper stage 201 and the lower stage 202 of the die sets, the stampers 35 and 36 are respectively fixed to middle stages 204 which are held movably along a guide pole 203. At this moment, the stampers 35 and 36 are held on the die sets in a state where the respective micro-lens array patterns are subjected to adjustment of optical axes. In the above arrangement, first, the glass substrates 37 and 38 are fixed respectively on the upper stage 201 and the lower stage 202 (FIG. 8a). Secondly, the first ultraviolet-hardening resins 39 are supplied respectively on the stamper 35 and the glass substrate 38 (FIG. 8b), the glass substrate 37 and the stamper 36 are caused to move closer to the stamper 35 and the glass substrate 38, respectively. At this moment, the upper stage 201 and the stampers 35 and 36 are moved in the direction of the lower stage 202 while the lower stage 202 is kept fixed. Then, each of the first ultraviolet-hardening resin 39 spreads between the glass substrate and the stamper (FIG. 8c), and each of the first ultraviolet-hardening resin 39 is hardened by ultraviolet irradiation. Thereafter, the glass substrate 37 and the stamper 36 are separated respectively from the stamper 35 and the glass substrate 38 (FIG. 8d), thereby forming the first micro-lens array 32 and the second micro-lens array 33 on the glass substrates 37 and 38, respectively. Next, the stampers 35 and 36 are removed from the die sets, and the second ultraviolet-hardening resin 40 is supplied on the second micro-lens array 33 that has been formed on the glass substrate 38 (FIG. 8e). Then, the upper stage 201, on which the glass substrate 37 formed with the first micro-lens array 32 is fixed, is caused to move closer to the lower stage 202 so as to spread the second ultraviolet-hardening resin 40 between the first micro-lens array 32 and the second micro-lens array 33 (FIG. 8f). The second ultraviolet-hardening resin 40 is hardened by ultraviolet irradiation, thereby manufacturing a micro-lens array substrate. Such a manufacturing method allows adjusting optical axes and inclination of micro-lens arrays.
However, the first and second manufacturing methods using the die sets cause the following problems.
In the first method, after the micro-lens arrays 32 and 33 are formed respectively on the glass substrates 37 and 38, the glass substrates 37 and 38 are fixed to the die sets. This needs an independent apparatus for forming micro-lens arrays, thus causing a problem of increase in apparatus manufacturing cost. In addition to the above problem, the first method requires adjustment of optical axes every time the glass substrate 37 on which the first micro-lens array 32 is formed and the glass substrate 38 on which the first micro-lens array 33 is formed are joined together. This needs long hours to manufacture a micro-lens array substrate. Therefore, the first method is unfavorable to mass production of a micro-lens array substrate.
Next, in the second. method, manufacturing a micro-lens array substrate is possible in one apparatus. However, after the stampers 35 and 36 are removed from the die sets to join the glass substrates 37 and 38 together, alignment of the stampers 35 and 36 is necessary when they are mounted on the die sets again because the stampers 35 and 36 are provided separately. Therefore, as in the case of the first method, the second method is unfavorable to mass production of a micro-lens array substrate. Moreover, distances between the glass substrate 37 and the stamper 35 and between the glass substrate 38 and the stamper 36 must be increased to remove the stampers 35 and 36, increasing a moving distance of the upper stage 201 and the stamper 35 inside the die sets. This could increase deviation in optical axes and inclination of micro-lens arrays caused during movement of the upper stage 201 and the stamper 35.